body{
    margin: 0 auto;
    width: 100%;
    height: 100%;
    overflow-x: hidden;
}
#header{
    width: 100%;
    height: 40px;
}
#header div{
    width: 25%;
    text-align: center;
    line-height: 40px;
    float: left;
    color: aliceblue;
    background: #000;
}